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Agricultural Science Paper 2, Nov/Dec 2008  
Questions: 1 2 3 4 5 6 7 8 9 10 Main
General Comments

Question 6

(a) With the aid of a diagram, describe the life cycle of cassava mealybug.                                                                                                                                 (6 marks)

(b) Discuss the cowpea beetle under the following headings:
(i)   mode of feeding;                                                                       (2 marks)
(ii)  nature of damage done.                                                             (2 marks)
(c)  State four measures that a farmer can take to control insect-pests
      of stored grains.                                                                               (4 marks)
(d)   Name two other storage insect-pests of grains.                     (2 marks)


This question was poorly attempted by the candidates.  In 6(a), many candidates could not describe the life cycle of cassava mealybug with the aid of a diagram.  Also in 6(b), most of the candidates were unable to discuss the cowpea beetle under mode of feeding and nature of damage done.

In 6(c) and (d), some candidates could neither state measures that a farmer can take to control insect-pests of stored grains nor name other storage insect-pests of grains.

The expected answers include:










  • The female lays eggs in a cottony sac;
  • Reproduction in this insect is pathenogenetic without the presence
       of males;
  • The eggs hatch into larvae which are wind borne;
  • The larvae pass through three instar stages before becoming adults;
  • One generation is completed in about 22 days.

Cowpea beetle:

(i)   Mode of feeding

(ii) Nature of damage done

     -      Larvae bore holes on the seeds/grains;
      -     Larvae destroy the embryo and reduce viability of seeds/grains;
      -     Larvae feed on the seeds/grains.

Control of Insect-pests of stored grains:

  • Concrete floors should be used to block insects hiding places;
  • Timely harvesting and if possible removal of infested grains before storage;     
  • Proper drying of grains before storage;
  • Stores should be well ventilated, but water proof and damp proof/Metal roofs
       should be used and not thatched roofs;
  • Do not store products close to the walls or directly on the floors;
  • Leave spaces between grain bags;
  • Inspect store regularly to detect and control pests infestation;
  • Fumigate store before storage and after removing the old stock or consignment;
  • Local storage methods such as the use of hot pepper/neem seeds/leaf extracts/neem
       seed oil/smoking could be adopted.

Storage Insect-pests of grains:

    • Sitophilus oryzae/Rice weevils;
    • Sitophilus zea mays/Maize weevils;
    • Large grain beetle;
    • Groundnut bruchid;
    • Sorghum/Guinea corn weevils.
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